Extend medial axis endpoints to fill the entire length. Includes fix for a minor memory leak caused by usage of old signature for Line::point_at()

xs/src/ExPolygon.cpp

@@ -148,6 +148,12 @@ ExPolygon::medial_axis(double max_width, double min_width, Polylines* polylines)
     // compute the Voronoi diagram
     ma.build(polylines);
     
+    // extend initial and final segments of each polyline (they will be clipped)
+    for (Polylines::iterator polyline = polylines->begin(); polyline != polylines->end(); ++polyline) {
+        polyline->extend_start(max_width);
+        polyline->extend_end(max_width);
+    }
+    
     // clip segments to our expolygon area
     intersection(*polylines, *this, *polylines);
 }